Drainage tubes, often simply called splint tubes and made of elastic material, have long been known in medicine and they serve to hold open narrowed body organs and facilitate the passage of body fluids or flushing fluids from one cavity into another, or to the outside. A very frequent area of application for such drainage tubes is the splinting of the ureter. In this splinting of the ureter urine is passed from the kidney pelvis into the bladder or the splinting also shunts the urethra and it conducts the urine from the kidney pelvis by way of the ureter, the bladder, and the urethra to the outside. For the securing of the drainage tube it has proved very helpful to prevent the sliding of the drainage tube out of the kidney pelvis, and insure its maintenance therein, by means of an inherent curvature of the tip of the drainage tube. For their introduction, these drainage tubes which because of their curved shape are known as "pigtail" splint tubes, must be brought into a straightened stretched form. The inherent curvature of the tip and of the end of the drainage tube is evened out by a relatively stiff mandrin. This mandrin has an additional task. It serves for the insertion of an auxiliary tube. As a rule, one end of the drainage tube lies in the kidney pelvis and the other end lies in the bladder. The placement of such a splint tube takes place with the aid of a cystoscope. The surgeon introduces the cystoscope through the urethra into the bladder, optically locates the outlet of the ureter and shoves the tip of the drainage tube through the ureter outlet into the ureter and subsequently slides the drainage tube upwardly and thus in the direction of the kidney until the tip of the drainage tube comes to lie in the kidney pelvis. For this introduction process into the ureter the drainage tube tip which because of its inherent curvature is bent around, must be straightened and this is effected by a stiff mandrin. In order to place the drainage tube (sleeve) 22 which is slightly longer than the ureter, in such a way that the curvature of the drainage tube in the range of the drainage tube tip lies in the kidney pelvis and the curvature in the range of the drainage tube end lies in the bladder, a second little tube, that is, an "auxiliary splint tube" is required. This auxiliary splint tube upon initial placement of the drainage tube over the mandrin is also slid onto the mandrin and it makes it possible to advance the drainage tube end through the cystoscope shaft into the bladder. The mandrin also avoids, for the introduction process, the inherent curvature of the drainage tube end, which curvature is to prevent that the end of the drainage tube pulls itself completely into the ureter.